1. Technical Field of the Invention
The present invention relates generally to tire inflation pressure detecting apparatuses for detecting the inflation pressures of tires on a vehicle and tire location detecting apparatuses for automatically detecting the locations of tires on a vehicle. More particularly, the invention relates to a direct-type tire inflation pressure detecting apparatus which has a function of wheel identification.
2. Description of the Related Art
A direct-type tire inflation pressure detecting apparatus generally includes a plurality of transmitters (or transceivers) and a receiver.
Each of the transmitters is directly mounted on one of a plurality of wheels of a vehicle and includes a pressure sensor for sensing the inflation pressure of a tire fitted on the wheel. Each of the transmitters is configured to transmit a pressure signal representative of the inflation pressure of the tire sensed by the pressure sensor.
The receiver is mounted on the body of the vehicle and includes at least one antenna. The receiver is configured to receive, via the antenna, the pressure signals transmitted from the transmitters and determine the inflation pressures of the tires based on the received pressure signals.
In the above apparatus, the receiver may also receive pressure signals transmitted by external transmitters (e.g., transmitters mounted on wheels of other vehicles). However, it is impossible for the receiver to determine whether a pressure signal received thereby has been transmitted by one of the transmitters of the apparatus or by an external transmitter. Moreover, it is also impossible for the receiver to detect the locations of the transmitters (or the locations of the associated tires) on the vehicle. In other words, the receiver cannot identify the wheel on which the transmitter having transmitted a pressure signal and the tire whose inflation pressure is indicated by the pressure signal are located.
To solve the above problems, as disclosed in U.S. Pat. No. 5,602,524, each of the transmitters may be further configured to transmit an identification signal (to be referred to as ID signal hereinafter) representative of the identity thereof along with the pressure signal. On the other hand, the receiver may be further configured to have reference ID signals registered therein, each of which coincides with the ID signal of one of the transmitters and is associated with the location of that transmitter.
Thus, the receiver can compare an ID signal received thereby with the reference ID signals registered therein and identify the transmitter which has transmitted the ID signal when the ID signal coincides with one of the reference ID signals.
Consequently, the receiver can identify the wheel on which the identified transmitter is mounted. More specifically, the receiver can determine whether the wheel is a FR (front-right), a FL (front-left), a RR (rear-right), or a RL (rear-left) wheel of the vehicle. Further, the receiver can determine the inflation pressure of the tire fitted on the identified wheel based on the pressure signal received along with the ID signal.
However, with the above configuration, it is required to previously register the ID signals specific to the respective transmitters as reference ID signals in the receiver through associating the ID signals with the locations of the respective transmitters on the vehicle (i.e., the wheels on which the respective transmitters are mounted). Moreover, as tire replacement or rotations are performed, it is required to update the reference ID signals in the receiver.
Conventionally, the registration of the ID signals in the receiver is made through a time-consuming manual operation. Thus, it is desired to automatically make the ID registration. Further, for automatically making the ID registration, it is desired to automatically detect the locations of the transmitters, in other words, to automatically identify the wheel on which each of the transmitters (or each of the associated tires) is located.
To meet the above desires, US Patent Application Publication No. 2007/0008097 A1 discloses a wheel identifying apparatus. This apparatus includes a plurality of transceivers, each of which is located on one of a plurality of wheels of a vehicle, at least one triggering device that is mounted on the body of the vehicle at different distances from the transceivers, and a receiver located on the body of the vehicle. The triggering device transmits a trigger signal whose strength attenuates with increase in the distance from the triggering device. Therefore, the strengths of the trigger signal at the transceivers are different from each other. In response to receipt of the trigger signal, each of the transceivers determines the strength of the trigger signal thereat and transmits a response signal which conveys signal strength information on the determined strength of the trigger signal. The receiver receives the response signals transmitted by the transceivers and identifies, for each of the received response signals, the wheel on which the transceiver having transmitted the response signal is located based on the signal strength information conveyed by the response signal.
Further, as an application to a four-wheel vehicle, the wheel identification apparatus includes a first triggering device and a second triggering device. The first triggering device is mounted on the body of the vehicle closer to the front wheels of the vehicle than the rear wheels, so as to transmit a first trigger signal only to the transceivers located on the front wheels (i.e., the FR and FL wheels). Further, the first triggering device is mounted at different distances from the front wheels, so that strengths of the first trigger signal at the transceivers on the front wheels are different from each other. Thus, the receiver can identify, for each of the transceivers on the front wheels, the wheel on which the transceiver is located based on the strength of the first trigger signal at the transceiver. On the other hand, the second triggering device is mounted on the body of the vehicle closer to the rear wheels of the vehicle than the front wheels, so as to transmit a second trigger signal only to the transceivers located on the rear wheels (i.e., RR and RL wheels). Further, the second triggering device is mounted at different distances from the rear wheels, so that strengths of the second trigger signal at the transceivers on the rear wheels are different from each other. Thus, the receiver can identify, for each of the transceivers on the rear wheels, the wheel on which the transceiver is located based on the strength of the second trigger signal at the transceiver.
With the above configuration, however, when a spare wheel is provided on the body of the vehicle in the vicinity of the rear wheels and also has a transceiver mounted thereon, the second trigger signal may be received by all the three transceivers on the rear and spare wheels. In this case, since the strength of the second trigger signal at the spare wheel is not so different from those at the transceivers on the rear wheels, it is difficult for the receiver to distinguish the three transceivers on the rear and spare wheels based on the strengths of the second trigger signal thereat.
Japanese Patent No. 3815305 discloses a tire pressure monitoring system which can determine whether a transmitter is located on a running or spare wheel of a vehicle. More specifically, in this system, each of all the transmitters on the running and spare wheels of the vehicle includes a rotation detecting means which detects rotation of the corresponding wheel by detecting a centrifugal force and outputs a rotation signal indicative of whether the corresponding wheel is rotating or not. Thus, a controller located on the body of the vehicle can determine, for each of all the transmitters, whether it is located on one of the running wheels or the spare wheel of the vehicle based on the rotation signal output from the transmitter.
However, in general, when the vehicle is running at a speed lower than 30 km/h, it is difficult to detect the centrifugal force and thus difficult to distinguish the transmitter on the spare wheel from those on the running wheels of the vehicle based on the rotation signals output from the transmitters.